Data Structures - Linked List Other Related Topics
Data Structures - Linked List Other Related Topics

Linked List - Delete the first node

In this method, the first node of the linked list is deleted. For example - if the given list is 10->20->30->40 and the first node is deleted, the list becomes 20->30->40.

Deleting the first node of the linked list is very easy. If the head is not null then create a temp node pointing to head and move head to the next of head. Then delete the temp node.

Linked List - Delete First Node

The function pop_front is created for this purpose. It is a 3-step process.

void pop_front() {
  if(head != NULL) {
    
    //1. if head is not null, create a
    //   temp node pointing to head
    Node* temp = head;

    //2. move head to next of head
    head = head->next; 

    //3. delete temp node
    free(temp); 
  }
}

void pop_front(struct Node** head_ref) {
  if(*head_ref != NULL) {
    
    //1. if head is not null, create a
    //   temp node pointing to head
    struct Node *temp = *head_ref;
     
    //2. move head to next of head
    *head_ref = (*head_ref)->next;

    //3. delete temp node
    temp = NULL;  
  }    
}

def pop_front(self):
  if(self.head != None):
    
    #1. if head is not null, create a
    #   temp node pointing to head
    temp = self.head
    
    #2. move head to next of head
    self.head = self.head.next 
    
    #3. delete temp node
    temp = None 

void pop_front() {
  if(this.head != null) {
    
    //1. if head is not null, create a
    //   temp node pointing to head
    Node temp = this.head;
    
    //2. move head to next of head
    this.head = this.head.next;
    
    //3. delete temp node
    temp = null;  
  }
}

public void pop_front() {
  if(this.head != null) {
    
    //1. if head is not null, create a
    //   temp node pointing to head
    Node temp = this.head;
    
    //2. move head to next of head
    this.head = this.head.next;
    
    //3. delete temp node
    temp = null;  
  }
}

public function pop_front() {
  if($this->head != null) {
    
    //1. if head is not null, create a
    //   temp node pointing to head
    $temp = $this->head;
    
    //2. move head to next of head
    $this->head = $this->head->next;
    
    //3. delete temp node
    $temp = null;  
  }
}

The below is a complete program that uses above discussed concept of deleting the first node of the linked list.

#include <iostream>
using namespace std;

//node structure
struct Node {
    int data;
    Node* next;
};

class LinkedList {
  private:
    Node* head;
  public:
    LinkedList(){
      head = NULL;
    }
 
    //Add new element at the end of the list
    void push_back(int newElement) {
      Node* newNode = new Node();
      newNode->data = newElement;
      newNode->next = NULL; 
      if(head == NULL) {
        head = newNode;
      } else {
        Node* temp = head;
        while(temp->next != NULL)
          temp = temp->next;
        temp->next = newNode;
      }    
    }

    //Delete first node of the list
    void pop_front() {
      if(head != NULL) {
        Node* temp = head;
        head = head->next; 
        free(temp); 
      }
    }

    //display the content of the list
    void PrintList() {
      Node* temp = head;
      if(temp != NULL) {
        cout<<"The list contains: ";
        while(temp != NULL) {
          cout<<temp->data<<" ";
          temp = temp->next;
        }
        cout<<"\n";
      } else {
        cout<<"The list is empty.\n";
      }
    }   
};

// test the code 
int main() {
  LinkedList MyList;

  //Add four elements in the list.
  MyList.push_back(10);
  MyList.push_back(20);
  MyList.push_back(30);
  MyList.push_back(40);
  MyList.PrintList();
  
  //Delete the first node
  MyList.pop_front();
  MyList.PrintList();  
  return 0; 
}

The above code will give the following output: 

The list contains: 10 20 30 40
The list contains: 20 30 40  

#include <stdio.h>
#include <stdlib.h>

//node structure
struct Node {
  int data;
  struct Node* next;
};

//Add new element at the end of the list
void push_back(struct Node** n, int newElement) {  
  struct Node *newNode, *temp;
  newNode = (struct Node*)malloc(sizeof(struct Node)); 
  newNode->data = newElement;  
  newNode->next = NULL;
  if(*n == NULL) {
    *n = newNode; 
  } else {
    temp = *n;
    while(temp->next != NULL) {
      temp = temp->next;
    }    
    temp->next = newNode;
  }
}

//Delete first node of the list
void pop_front(struct Node** head_ref) {
  if(*head_ref != NULL) {
    struct Node *temp = *head_ref;
    *head_ref = (*head_ref)->next;
    temp = NULL;  
  }    
}

//display the content of the list
void PrintList(struct Node* head_ref) {
  struct Node* temp = head_ref;
  if(head_ref != NULL) {
    printf("The list contains: ");
    while (temp != NULL) {
      printf("%i ",temp->data);
      temp = temp->next;  
    }
    printf("\n");
  } else {
    printf("The list is empty.\n");
  }   
}

// test the code 
int main() {
  struct Node* MyList = NULL;

  //Add four elements in the list.
  push_back(&MyList, 10);
  push_back(&MyList, 20);
  push_back(&MyList, 30);
  push_back(&MyList, 40);
  PrintList(MyList);

  //Delete the first node
  pop_front(&MyList);
  PrintList(MyList);
  return 0; 
}

The above code will give the following output: 

The list contains: 10 20 30 40
The list contains: 20 30 40 

# node structure
class Node:
  def __init__(self, data):
    self.data = data
    self.next = None

#class LinkedList
class LinkedList:
  def __init__(self):
    self.head = None

  #Add new element at the end of the list
  def push_back(self, newElement):
    newNode = Node(newElement)
    if(self.head == None):
      self.head = newNode
      return
    else:
      temp = self.head
      while(temp.next != None):
        temp = temp.next
      temp.next = newNode

  #Delete first node of the list
  def pop_front(self):
    if(self.head != None):
      temp = self.head
      self.head = self.head.next 
      temp = None  

  #display the content of the list
  def PrintList(self):
    temp = self.head
    if(temp != None):
      print("The list contains:", end=" ")
      while (temp != None):
        print(temp.data, end=" ")
        temp = temp.next
      print()
    else:
      print("The list is empty.")

# test the code                 
MyList = LinkedList()

#Add four elements in the list.
MyList.push_back(10)
MyList.push_back(20)
MyList.push_back(30)
MyList.push_back(40)
MyList.PrintList()

#Delete the first node
MyList.pop_front()
MyList.PrintList()

The above code will give the following output: 

The list contains: 10 20 30 40
The list contains: 20 30 40 

//node structure
class Node {
    int data;
    Node next;
};

class LinkedList {
  Node head;

  LinkedList(){
    head = null;
  }

  //Add new element at the end of the list
  void push_back(int newElement) {
    Node newNode = new Node();
    newNode.data = newElement;
    newNode.next = null; 
    if(head == null) {
      head = newNode;
    } else {
      Node temp = new Node();
      temp = head;
      while(temp.next != null)
        temp = temp.next;
      temp.next = newNode;
    }    
  }

  //Delete first node of the list
  void pop_front() {
    if(this.head != null) {
      Node temp = this.head;
      this.head = this.head.next;
      temp = null;  
    }
  }

  //display the content of the list
  void PrintList() {
    Node temp = new Node();
    temp = this.head;
    if(temp != null) {
      System.out.print("The list contains: ");
      while(temp != null) {
        System.out.print(temp.data + " ");
        temp = temp.next;
      }
      System.out.println();
    } else {
      System.out.println("The list is empty.");
    }
  }    
};

// test the code
public class Implementation { 
  public static void main(String[] args) {
    LinkedList MyList = new LinkedList();

    //Add four elements in the list.
    MyList.push_back(10);
    MyList.push_back(20);
    MyList.push_back(30);
    MyList.push_back(40);
    MyList.PrintList(); 

    //Delete the first node
    MyList.pop_front();
    MyList.PrintList();  
  }
}

The above code will give the following output: 

The list contains: 10 20 30 40
The list contains: 20 30 40 

using System;

//node structure
class Node {
  public int data;
  public Node next;
};

class LinkedList {
  Node head;

  public LinkedList(){
    head = null;
  }
  
  //Add new element at the end of the list
  public void push_back(int newElement) {
    Node newNode = new Node();
    newNode.data = newElement;
    newNode.next = null; 
    if(head == null) {
      head = newNode;
    } else {
      Node temp = new Node();
      temp = head;
      while(temp.next != null)
        temp = temp.next;
      temp.next = newNode;
    }    
  }

  //Delete first node of the list
  public void pop_front() {
    if(this.head != null) {
      Node temp = this.head;
      this.head = this.head.next;
      temp = null;  
    }
  }

  //display the content of the list
  public void PrintList() {
    Node temp = new Node();
    temp = this.head;
    if(temp != null) {
      Console.Write("The list contains: ");
      while(temp != null) {
        Console.Write(temp.data + " ");
        temp = temp.next;
      }
      Console.WriteLine();
    } else {
      Console.WriteLine("The list is empty.");
    }
  }     
};

// test the code
class Implementation { 
  static void Main(string[] args) {
    LinkedList MyList = new LinkedList();

    //Add four elements in the list.
    MyList.push_back(10);
    MyList.push_back(20);
    MyList.push_back(30);
    MyList.push_back(40);
    MyList.PrintList();   

    //Delete the first node
    MyList.pop_front();
    MyList.PrintList();  
  }
}

The above code will give the following output: 

The list contains: 10 20 30 40
The list contains: 20 30 40 

<?php
//node structure
class Node {
  public $data;
  public $next;
}

class LinkedList {
  public $head;

  public function __construct(){
    $this->head = null;
  }
  
  //Add new element at the end of the list
  public function push_back($newElement) {
    $newNode = new Node();
    $newNode->data = $newElement;
    $newNode->next = null; 
    if($this->head == null) {
      $this->head = $newNode;
    } else {
      $temp = new Node();
      $temp = $this->head;
      while($temp->next != null) {
        $temp = $temp->next;
      }
      $temp->next = $newNode;
    }    
  }

  //Delete first node of the list
  public function pop_front() {
    if($this->head != null) {
      $temp = $this->head;
      $this->head = $this->head->next;
      $temp = null;  
    }
  }

  //display the content of the list
  public function PrintList() {
    $temp = new Node();
    $temp = $this->head;
    if($temp != null) {
      echo "The list contains: ";
      while($temp != null) {
        echo $temp->data." ";
        $temp = $temp->next;
      }
      echo "\n";
    } else {
      echo "The list is empty.\n";
    }
  }   
};

// test the code 
$MyList = new LinkedList();

//Add four elements in the list.
$MyList->push_back(10);
$MyList->push_back(20);
$MyList->push_back(30);
$MyList->push_back(40);
$MyList->PrintList();

//Delete the first node
$MyList->pop_front();
$MyList->PrintList(); 
?>

The above code will give the following output: 

The list contains: 10 20 30 40
The list contains: 20 30 40
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